Method of detecting pressure uniformity

ABSTRACT

An improved method is disclosed for detection of pressure uniformity between adjacent, contacting, pressurized surfaces which comprises the placement of a sheet with a low density bulking agent therein in the &#39;&#39;&#39;&#39;nip&#39;&#39;&#39;&#39; of said surfaces, placing them into pressurized contact, and denoting the degree of deformation or loss of caliper across the sheet. The degree of deformation being directly related to the amount of pressure, thus providing a means of quantitatively denoting &#39;&#39;&#39;&#39;pressure&#39;&#39;&#39;&#39; points between said surfaces as well as doing so with a greater degree of sensitivity than prior art techniques and having application in the fields of paper manufacture, printing, and reprography.

United States Patent [191 Wieloch Jan. 21, 1975 METHOD OF DETECTING PRESSURE UNIFORMITY [75] Inventor: Francis John Wieloch, Penfield,

[73] Assignee: Xerox Corporation, Stamford,

Conn.

[22] Filed: Oct. 26, 1972 [21] Appl. No.: 301,023

[52] U.S. Cl 73/88 R [51] Int. Cl. G0ln 33/00 [58] Field of Search 73/88 R, 94; 33/182; 100/99; 162/263 [56] References Cited UNITED STATES PATENTS 3,041,735 7/1962 Allen 33/174 R 3,396,577 8/1968 Brackett 73/141 R FOREIGN PATENTS OR APPLICATIONS 10,350 4/1912 Great Britain 73/141 R Primary ExaminerJerry W. Myracle Attorney, Agent, or Firm]ames .l. Ralabate; James P. OSullivan; Donald M. MacKay [57] ABSTRACT An improved method is disclosed for detection of pressure uniformity between adjacent, contacting, pressurized surfaces which comprises the placement of a sheet with a low density bulking agent therein in the nip of said surfaces, placing them into pressurized contact, and denoting the degree of deformation or loss of caliper across the sheet. The degree of deformation being directly related to the amount of pressure, thus providing a means of quantitatively denoting pressure points between said surfaces as well as doing so with a greater degree of sensitivity than prior art techniques and having application in the fields of paper manufacture, printing, and reprography.

5 Claims, 1 Drawing Figure PATENTED m1 ms v 0- v w 2 2 m AVERAGE PRESSURE (PLI) METHOD OF DETECTING PRESSURE UNIFORMI'IY BACKGROUND OF THE INVENTION This invention generally relates to an improved means of measuring the pressure uniformity between two adjacent contacting surfaces.

In paper manufacturing, in general, several operations exist which call for the action of pressurized rollers or surfaces on the formed paper fibers, including pressing for water removal and calendering for surficial improvement of the formed sheet in order to facilitate character printing thereon. The rollers may be in sequential contact with the paper or paper fibers and are actuated into pressurized contact by means of various hydraulic or pneumatic pressure type systems. The line of contact between the two rolls, either press, calender or super calender rolls is referred to as the nip between the rolls. Consequently, the degree of pressure exerted between these two surfaces when they are in pressurized contact is referred to as the nip pressure.

A factor of particular importance insofar as surficial finishing operations on bond type of paper, is the uniformity of nip pressure, across the entire nip or line of contact between these two surfaces. If the degree of contact or the pressure is not uniform all the way across the nip, a paper or uneven surficial characteristics and limited printing acceptability is produced. Additionally, if the contacting rolls are employed during paper pressing, inefficient removal of moisture results thus producing an excessive burden on the drying operation of the manufacturing process to remove excess moisture.

Additionally, areas other than paper manufacturing, rely upon uniform pressure between adjacent contacting surfaces such as rolls, plates, etc., to provide certain functional results. For example, in xerographic printing or reproduction, after formation of a latent electrostatic image and powder development thereof with electrostatically adhering toner, fixing or fusion of the resultant powdered image can be carried out by various means including heat, pressure, or solvent vapors, as well as combinations thereof, particularly heat and pressure. It therefore may be seen that machine fusing configurations for xerographic or electrostatic printing may exist which necessitates adjacent pressurized surfaces having uniform pressure contact between these surfaces.

Heretofore, a limiting factor in the above mechanical configurations of adjacent pressure surfaces, has been in measuring the pressure uniformity across the line of contact or nip pressure. It cannot always be determined prior to machine operation whether or not nip pressure is uniform and consequently, needless time and effort as well as materials are expended after the machine is operative to adjust pressure contact between the surfaces and consequently improve nip pressure uniformity between these surfaces. Measurement of nip pressure has been carried out by utilizing either a cooperative laminate of carbon paper and ordinary white paper or a laminate of a pressure sensitive paper filled with rupturable ink capsules, and ordinary white paper. The laminate is placed between the adjacent pressure surfaces at various points and pressurized and uneven contact or excessive pressure is denoted by darker or wider smudges or darkened areas on the white paper.

Not only is such measurement means not very qualitative in nature, it denotes little as to degrees of differences in pressure. Furthermore, it lacks the sensitivity to measure subtle differences in pressure uniformity since the caliper of this type of paper changes very little in response to pressure, particularly when high pressures are involved.

The present invention has obviated difficulties such as those noted above with various prior art measurement techniques and provides an unexpectedly accurate means of detecting pressure differences between two adjacent pressurized surfaces, these differences previously having been incapable of measurement.

SUMMARY OF THE INVENTION The present invention therefore relates to an improved method for detecting pressure uniformity between two adjacent contacting surfaces and denoting areas of minimal as well as excessive pressure. The method comprises the placement between the adjacent contacting surfaces of a sheet of paper, the sheet comprising paper making fibers having incorporated therein a low density bulking agent in a proportion of up to about 10 percent by weight of said fibers, followed by pressurizing the nip between these two surfaces and recording the loss in caliper across the described sheet at various points with the greater loss in caliper corresponding to areas on the contacting surfaces of higher pressure.

Alternatively, the described paper may be used cooperatively in the form of a laminate with a paper having a colored transferable material thereon to transfer color to the described sheet in those areas of higher pressure between said surfaces.

The above described paper having a low density bulking agent, such as a gaseous filled thermoplastic microspheres, has been found to be more pressure sensitive than other papers which have heretofore been available for this purpose and the use thereof consequently results in a highly desirable means for measuring pressure uniformity at the nip between adjacent contacting pressure surfaces.

It is a further object of the instant invention to measure pressure uniformity to a degree which was heretofore not obtainable with various prior art papers.

It is also an object of the instant invention to devise a meaningful test for pressure uniformity between adjacent pressure surfaces having general applicability in the areas of paper manufacturing, printing, and reprography.

BRIEF DESCRIPTION OF THE DRAWING The FIGURE depicts the pressure sensitivity of the process of the instant invention utilizing the paper as set out herein as compared to various prior art papers.

DESCRIPTION OF THE PREFERRED EMBODMENTS The paper used in the instant invention as a means for detecting pressure uniformity between two adjacent surfaces comprises conventional paper making fibers having incorporated therein, a low density bulking agent in an amount up to about 10 percent by weight of said fibers. The low density bulking agent is a gaseous filled material which can fill the voids between the paper making fibers and consequently provide a paper of lighter weight, but also have a greater percentage of deformation than certain other prior art papers such as pressure sensitive paper having rupturable microspheres which are filled with an oil or ink type of material. The degree of deformation of this type of paper makes it highly responsive to applied pressure and thus provides a suitable and acceptable means for measuring pressure uniformity between contacting, adjacent pressure surfaces.

The paper as employed in the pressure measuring means preferably comprises a formed paper or moving web of paper having incorporated therein gaseous filled spheres of thermoplastic resins, said paper being generally described in U.S. Pat. No. 3,293,114. The present invention is not however intended to be limited to the particular type of low density bulking agent or materials comprising the same, and any including those in the above described patent as well as other gaseous filled microspheres may be employed, as long as said microspheres are of the same order of density.

The percentage of the low density bulking agent gaseous filled microspheres employed in the present invention is in an amount of up to percent by weight of the paper making fibers and are added prior to sheet formation in the wet pulp section of the machine, prior to deposition of the sheet on a Fourdrinier screen or on the collecting surface of a cylinder machine. These microspheres are deposited in the created voids between the paper fibers to provide a paper of lighter weight and increased caliper. Consequently, the increased caliper, also permits a large percentage of the sheet to be deformed when pressure is applied thus resulting in the useful application which is set out as follows.

The described sheet may be used to measure pressure uniformity at the nip pressure between adjacent pressure surfaces by placing the described sheet in the nip between the contacting surfaces and then pressurizing the surfaces into complete pressure contact to simulate operative pressures between the two surfaces during machine operation.

Additionally, if desired, the described paper could be fed between the surfaces while they are in operation, thus obviating a further disadvantage of prior art measurement devices such as carbon paper, which could not be employed in such a manner.

Prior to insertion of the sheet in the nip of the pressurized surfaces, the general caliper of the sheet is measured at selected spots on the sheet to generally encompass the entire sheet area. Obviously, the larger the sheet employed, the more areas that should be selected for caliper measurements to provide an accurate representation of sheet deformation following pressure contact. The caliper or thickness of the selected areas, including areas at each extreme of the sheet, and at the middle are then measured with a micrometer or any thickness measuring device prior to insertion of the sheet between the surfaces. The area of measurement is generally indicated by marking and following insertion into the nip of the surfaces, the caliper at the same area is measured and recorded, and loss in caliper measured because of pressure contact with the surfaces. The degree of deformation or loss in caliper is of course, directly related to the applied pressure thus resulting in easy measurement of the areas of higher pressure between the surfaces.

Insofar as possible, it is preferable that the atmospheric conditions of the test on a day to day basis be normalized for humidity and temperature variations to provide a daily consistency between readings. However, since only pressure points" at the nip are being measured, the appearance of an excessive pressure point at the nip of the two surfaces denotes a need for adjustment. Also, in the event heated surfaces are employed, it is preferable to keep the temperature reasonably constant, since the degree of deformation can be related to the temperature of the surfaces, although differences of deformation or pressure points are proportional to the temperature and can therefore be easily measured without control of the temperature of the pressurized surfaces.

An alternative embodiment of this instant invention comprises the use of the described paper as a laminate with a paper having a transferable colored dye thereon, such as carbon paper for a qualitative type of measurement, of pressure points at the nip of adjacent surfaces. Although quantitative measurement is not as likely using this technique, it does provide a quick visual illustration of various pressure points at the nip of the surfaces. The wider the colored area which results on the described paper because of the transferred dye, the more pressure that exists at that point.

It may therefore be seen that described is a useful measurement technique obviating several disadvantages of the prior art and the following examples are further set forth to illustrate more completely the instant invention.

EXAMPLE 1 Samples of paper including the following were employed in a comparative test against paper prepared as generally described in U.S. Pat. No. 3,293,114 having about 10 percent by weight of a low density bulking agent such as gaseous filled thermoplastic microspheres incorporated therein. The samples of paper included conventional papers such as Xerox 4024 papers, Consolith Opaque, and a special printing paper with 78 percent groundwood pulp produced by Great Northern Paper Co.

Sheets of each of the above types of paper, each sheet having a total of 12 numbered areas, were employed in the test which utilized two adjacent pressure rolls 3% inches in diameter as the pressure contacting surfaces. All of the sheets of paper were equilibrated at least 24 hours at 73 F and 50 percent relative humidity before caliper measurements were obtained on each sheet at the designated areas, using a Model 549 Micrometer as manufactured by Testing Machines lnc., Amityville, N.Y.

Following the initial caliper measurements, each sample of paper was fed through the pressurized rolls at varying pressures including 50, 100, 200, 300, 400 and 500 pounds per linear inch, and calipher measurements were again made on the marked areas. The loss in caliper was determined and expressed as a percentage of the original paper caliper, which was then averaged for the entire sheet. The roller speed was held constant for the test at 8 inches per second.

Referring now to the FIGURE, in which is illustrated in graphic formation the described samples and the percent loss in caliper obtained on each sheet.. lt may be seen that at selected pressures of and 500 pli, the loss of caliper on the described paper (A) was about 25 and 45 percent respectively while for the Consolith Opaque (B), the Xerox 4024 (C), and the Great Northern Paper (D) (78 percent groundwood),

it was 7 percent, 2 percent, and 1 percent respectively at 100 pli and 21 percent, percent and 9 percent at 500 pli. It may he therefore seen that the pressure sensitive paper of the instant invention comprises a pressure uniformity measurement means of greater sensitivity than the prior art papers, consequently, subtle differences in pressure which are not easily measured by these prior art papers are easily measured varying the paper with the low density bulking agent because of the greater percentage deformation of loss of caliper of this paper upon exposure to pressure. Areas of higher pressure may be therefore easily determined at various points on the nip of the two pressurized contacting surfaces.

While the foregoing example is merely illustrative of the instant invention, the disclosure as set out herein is intended to include all reasonable equivalents, modifications, and steps which can reasonably be considered within the scope, limited only by the appended claims.

What is claimed is:

l. A method of detecting pressure uniformity between adjacent contacting pressure surfaces comprismg:

a. placing between said contacting surfaces a sheet of paper which comprises paper making fibers having incorporated therein a low density bulking agent in an amount of up to about 10 percent by weight of said fibers;

b. pressurizing the surfaces into pressurized contact to cause deformation of said paper in areas of higher pressure between said surfaces whereby a loss of caliper occurs across said sheet, the loss in caliper corresponding to areas on said contacting surfaces of higher pressure; and

c. measuring the deformed paper.

2. A method as set forth in claim 1 wherein said paper comprises a sheet having up to about 10 percent by weight of gaseous filled thermoplastic spheres incorporated in said sheet.

3. A method as set forth in claim 1 where said sheet is fed between said contacting surfaces while said surfaces are in pressurized contact.

4. A method of detecting pressure uniformity between adjacent, contacting pressure surfaces comprismg:

a. placing between said surfaces a composite sheet which comprises a first sheet consisting essentially of paper making fibers with a low density bulking agent therein, in a proportion of up to about l0 percent by weight of said fibers, and a second sheet of paper with a colored transferable material thereon,

b. pressing the surfaces into pressurized contact to cause deformation of said paper in areas of higher pressure between said surfaces and transfer colored material to said first sheet in said areas of higher pressure, thus denoting areas of higher pressure on said contacting surfaces, and measuring the differences in color density on said first sheet.

5. A method as set forth in claim 4 wherein said paper comprises a sheet having up to about 10 percent by weight of gaseous filled thermoplastic spheres incorporated in said sheets. 

1. A method of detecting pressure uniformity between adjacent contacting pressure surfaces comprising: a. placing between said contacting surfaces a sheet of paper which comprises paper making fibers having incorporated therein a low density bulking agent in an amount of up to abOut 10 percent by weight of said fibers; b. pressurizing the surfaces into pressurized contact to cause deformation of said paper in areas of higher pressure between said surfaces whereby a loss of caliper occurs across said sheet, the loss in caliper corresponding to areas on said contacting surfaces of higher pressure; and c. measuring the deformed paper.
 2. A method as set forth in claim 1 wherein said paper comprises a sheet having up to about 10 percent by weight of gaseous filled thermoplastic spheres incorporated in said sheet.
 3. A method as set forth in claim 1 where said sheet is fed between said contacting surfaces while said surfaces are in pressurized contact.
 4. A method of detecting pressure uniformity between adjacent, contacting pressure surfaces comprising: a. placing between said surfaces a composite sheet which comprises a first sheet consisting essentially of paper making fibers with a low density bulking agent therein, in a proportion of up to about 10 percent by weight of said fibers, and a second sheet of paper with a colored transferable material thereon, b. pressing the surfaces into pressurized contact to cause deformation of said paper in areas of higher pressure between said surfaces and transfer colored material to said first sheet in said areas of higher pressure, thus denoting areas of higher pressure on said contacting surfaces, and measuring the differences in color density on said first sheet.
 5. A method as set forth in claim 4 wherein said paper comprises a sheet having up to about 10 percent by weight of gaseous filled thermoplastic spheres incorporated in said sheets. 